The invention relates to a shielding device for a mounting rack for holding insertable, electrical modules. At least one outer wall of the device or component has a perforated, grounded shielding panel for electromagnetically shielding and conducting away heat from the device.
Such a mounting rack has been disclosed, for example, by WO 92/16093. According to this document, a shielding housing of a module rack is composed of aluminum sheet metal, and the upper and lower sides are embodied as perforated panels in order to conduct away heat from the mounting rack. Such aluminum sheets are, for example, 2 mm thick and have good electrical conductivity. The large thickness of the shielding panel produces favorable shielding conditions even when there is a high proportion of holes.
A disadvantage here is that the mounting rack cannot be exclusively fabricated from aluminum parts so that when it is disposed of the various materials have to be separated, which is costly.
EP 0351070 A, which corresponds to U.S. Pat. No. 4,872,090, discloses a shielding housing for an electrical module which has two walls lying opposite one another with each wall being formed from two perforated panels. The panels have ventilation holes offset with respect to one another, so that a very good shielding effect is achieved. However, the offset of the ventilation holes impedes the throughflow of the cooling air.
The present invention is based on the object of improving the shielding properties of the outer wall, cooling of the modules and reducing the cost of disposal.
These objects are achieved with a shielding device for a mounting rack for holding insertable electrical modules. At least one outer wall of the shielding device has two perforated, grounded shielding panels for electromagnetically shielding and conducting away heat from modules. The shielding panels extend at least approximately parallel to one another and at a distance from one another with an intermediate space between the two shielding panels being filled with an insulator against which the two shielding panels directly bear and the two shielding panels and the insulator have perforation patterns which are congruent with one another and are aligned with respect to one another.
The arrangement of two shielding panels which are parallel with one another and at a distance from one another improves the shielding effect of the outer wall considerably. Trials have shown that the shielding attenuation with an optimum arrangement and embodiment of the shielding panels is increased by more than 20 dB in comparison with a single panel. The double-walled construction enables the stability of the outer wall to be considerably increased. It is therefore possible to reduce the thickness of the panel without adversely affecting the increased shielding effect. As a result, it is possible to use other materials which can be more easily disposed of
It is now possible to manufacture the shielding panel from considerably thinner stainless steel or chrome steel. The other parts of the housing and the mounting elements can also be manufactured from this material so that such a mounting rack can be disposed of without difficulty.
The distance or intermediate space between the panels of one to eight times the thickness of a panel permits the shielding attenuation to be increased considerably. At the same time, the holes of the two shielding panels can be respectively arranged in an aligned fashion in order to improve ventilation without adversely affecting the shielding effect.
A particularly high level of shielding attenuation is achieved with a distance of only four times the thickness of the panel. This means that the shielding panels can be arranged at a relatively small distance from one another so that the outer dimensions of the mounting rack are increased only to a small extent.
The congruent perforation patterns of the two panels and the insulator reduce the number of disruptive edges and reduce the flow resistance between the two shielding panels considerably, so that the through flow rate of cooling air is increased but the shielding effect is not adversely affected.
The insulator is preferably a flat perforated panel, which is composed of foam material, which preferably has a laminated surface in the region of the perforations, is cost-effective to manufacture and easy to use.
The two shielding panels and the insulator are embodied as a sandwich, whose parts are connected to one another by a material and results in a particularly stable outer wall which permits the thickness of the panel to be reduced, accompanied by a high level of stability.